Conclusion

AN2678

14/16

4

Conclusion

By taking advantage of the analog calibration feature built into the new M41T82/83/93 family

of serial RTCs, a low cost clock with high accuracy across temperature can be achieved.

This approach requires only the use of the microprocessor timer to periodically measure the

RTC's true frequency. Initially, the analog calibration is adjusted at room temperature.

Then, periodic updates to the digital calibration register are made to compensate for any

RTC oscillator drift due to temperature changes which may occur. During the analog

calibration, a simple binary decision tree is employed which allows the user to fine tune the

clock's oscillator and zero out any frequency shift. Subsequent digital calibration

adjustments use a look-up-table.

Using this combination of analog and digital calibration enables the user to have a simple

periodic update scheme which requires low overhead while providing accurate timekeeping

and minimal cost.